Officers in helicopters, on bikes and on horses will try to keep the peace. In addition, the department has been visiting stores talking to managers about the psychology of the frantic shopper.

Black Friday is a day for burning off those Thanksgiving calories with some intense Christmas shopping. But for the Los Angeles Police Department, it's become a day of surveillance, crowd control and crime-suppression tactics.

Helicopters will buzz above some shopping centers, and below, a cavalry of LAPD officers will patrol on bikes and horses. From store rooftops, officers will scan the crowds below looking for unruly behavior. Electronic signs near stores will warn customers about becoming victims of theft as they navigate the mass of humanity looking for bargains.

The deployments are part of a new strategy by the LAPD to deal with the retail roller derby that comes after Thanksgiving. In addition to stationing officers around shopping centers, the LAPD has been visiting stores across the city this week, talking to managers about the psychology of the frantic shopper.

Officials said the push was prompted by a series of incidents at Black Friday sales, notably one last year at a Porter Ranch Wal-Mart in which two dozen people were injured when a woman unleashed pepper spray during a frantic battle for some discounted video games.

LAPD Cmdr. Andy Smith said he hopes people will behave. But "like Chief [Charlie] Beck says, we are not in the optimism business."

The LAPD would not say exactly how many officers it will deploy Friday, but the number is expected to be considerable. In the Valley divisions, for example, officials have put together detailed tactical plans for each major shopping center, using mobile command posts and both officers and cadets.

"For some people, shopping is a competitive sport," Smith said. "But it should not be a contact sport."

Even some big retailers — which for years fueled the shopping frenzy with aggressive marketing and deep discounts — are trying to rein in some of the excitement they create this year.

Fernando Reyes, manager of the Wal-Mart in Porter Ranch where the pepper spray incident occurred, said his main goal is to avoid a repeat of the chaos. He has met with the LAPD and plans new crowd-control strategies, including setting up special check-out lines for some sales items.

The store also plans to give out vouchers to shoppers for "door buster" merchandise to avoid people jockeying for the limited supplies. If a customer did not get such a voucher, Reyes said there should be a "reasonable expectation" that they won't get the sales item.

The LAPD has talked to other retailers about creating "time-specific entry passes" that would stagger the number of shoppers who are inside the store at any given time. In a flier the department is handing out to store managers, officials note that "this process has been very successful at many of the major theme parks and can help to ensure organized, safe entry into your business."

Despite all the headlines, Black Friday misbehavior is still relatively rare. Police report a scattering of brawls, assaults and various larcenies each year. But it's the headlines that people remember. A few years ago, gunfire erupted in a crowded Palm Desert Toys R Us, killing two people. Four years ago, a Long Island, N.Y., Wal-Mart employee was trampled to death by a crush of customers who toppled large glass doors.

Aimee Drolet Rossi, a consumer psychologist at UCLA's Anderson School of Management, said it should not be surprising that some people act out on Black Friday. Research on rats and monkeys has shown that they become more aggressive when placed in a crowded situation, and Rossi said humans are no different.

"Crowding leads people to behave less altruistically, in part because people's sense of responsibility lags when a lot of other people are around," she said. "People assume that other people will step up to help someone who is in distress."

She also said research shows that people are less likely to make eye contact with people in crowded situations, and this can cause them to make bad decisions.

Retailers bear some of the responsibility for what's happened, she said.

"They set up this environment that encourages this competitive shopping ...." Rossi said. "They offer only 10 TV sets at the ridiculously low price. It's really no surprise people get upset when they don't get one."

This year, some stores are actually opening on Thanksgiving Day, and people are already lined up.

Tony Juarez, a 30-year-old North Hollywood resident, has been camping outside the Porter Ranch Best Buy for a week. It's been an eight-year tradition for Juarez and his friends, who set up a makeshift campsite with portable chairs, blankets and a heater. A few feet away, other campers actually brought tents.

This year, Juarez is hoping to score some cut-priced TVs and laptops. A few years ago, he got a $200 Toshiba laptop and is still crowing about the bargain.

He was at the Best Buy when the pepper spray incident occurred at the Wal-Mart next door. He watched, stunned, as a stampede of shoppers streamed out of the store and scores of police arrived.

This year, he's definitely noticed more police presence at the shopping center, and that has been comforting.

"We are seeing an LAPD car every five minutes. It's definitely safer," he said.

But more police isn't enough for South L.A. resident Lynnette Jordan, who plans to stay away from the Baldwin Hills Crenshaw mall on Friday.

"You are still going to deal with folks basically fighting to get into the door to get the item they so desperately want," Jordan said. "No matter what, some people will act the fool because that's what they do."